I just picked up a rebuilt 2150 for my truck. I noticed it's different from the carb I had on it before. I have a 1976 ford f100. The carb I have now has a fuel bowl vent valve, which the original didn't have. Can I just cap/plug that vent off or should I route that somewhere?

 

Earlier Autolite carbs had that fuel bowl vent and even earlier ones had no vent. My 65 2100 doesn't while my 68 2100 does. The 68 has a small hole in the top with a rubber flap that can open and close over the top. Later a tube was used so you could vent the fumes over to a charcoal canister for emissions. Do you have the one pictured?

 

The fuel bowl needs to be vented to atmosphere, either directly or to a canister.

Believe the earlier style with no vent connection fitting has a small hole where the bowl is vented directly to atmosphere.

The 2150 carburetor on my 1976 F250 FE360 has no separate fuel bowl vent connection.